A 90-minute episode pulled in 10.12m (38.9%) from 8pm on Saturday, peaking with 12m (47.4%) in the final five minutes.
It easily topped the audience for BBC One's Strictly Come Dancing, which averaged 8.42m (33.9%) between 7pm and 9.15pm.
Earlier, the latest episode of Merlin put in 5.41m (28.4%) from 6.15pm, a week-on-week growth of around 350k. After Strictly, the Lottery draw was seen by 4.81m (19%) then a new episode of Casualty brought in 5.61m (25.7%).
Britain Does The Funniest Things pulled in 3.27m (18%) for ITV1 in the 6pm hour, then the final episode of gameshow The Cube averaged 4.38m (19.1%).
Channel 4's screening of The Lord of the Rings: Return of the King averaged 1.8m (7.6%) between 7.05pm and 10.50pm.
On BBC Two, The Three Lives Of Ghandi - a new three-part documentary about the life of the spiritual leader - interested 1.17m (4.4%) at 8.15pm, then an hour later, Monty Python - Almost The Truth: The BBC Lawyers' Cut appealed to 1.64m (7.2%). A screening of And Now For Something Completely Different... followed with 1.24m (8.1%).
A double-bill of NCIS logged 819k (3.4%) and 1.02m (3.9%) for Five from 7.20pm, then at 9.15pm, CSI: NY picked up 1.01m (4.4%). CSI grew the audience further to 1.19m (6.8%) an hour later, then Law & Order: SVU finished the night with 918k (9%).
Overall, BBC One was ahead in primetime with a share of 30.4% to ITV1's 26.5%. Channel 4 was third with 7.3% (+1: 0.9%), followed by BBC Two with 5.9% and Five with 4.3%.
Elsewhere, The Xtra Factor topped the multichannel ratings, albeit with a series low of 854k (4.3%) and 150k (1.1%) on timeshift.
BARB ratings data supplied by Attentional